docs(CONTRIBUTING): update contributing guide, add Slack invite link (#662)

Author: bibschan

CONTRIBUTING.md

@@ -1,9 +1,88 @@
-# Web Platform Incubator Community Group
+# Contributing to this repository
 
-This repository is being used for work in the W3C Web Platform Incubator Community Group, governed by the [W3C Community License
-Agreement (CLA)](http://www.w3.org/community/about/agreements/cla/). To make substantive contributions, you must join the CG.
+Thank you for contributing to the Web Monetization specification. Your contributions help shape emerging web standards.
 
-If you are not the sole contributor to a contribution (pull request), please identify all contributors in the pull request comment.
+## Before you begin
+
+- Have you read the [Code of Conduct](https://www.w3.org/policies/code-of-conduct/)?
+- Check out the [existing issues](https://github.com/WICG/webmonetization/issues) and see if we [accept contributions](#types-of-contributions) for your type of issue
+- (Optional) Join the Community Group and agree to the [W3C Community Contributor License Agreement (CLA)](http://www.w3.org/community/about/agreements/cla/)
+
+## Types of contributions
+
+You can contribute to the Web Monetization specification in several ways.
+
+### Discussions
+
+Discussions are where we have conversations about the specification and the broader ecosystem.
+
+If you have questions, new ideas, or want to explore something before opening an issue — [join the discussion](https://github.com/WICG/webmonetization/discussions).
+
+### Proposals & feature requests
+
+If you have an idea for improving the specification or introducing new functionality, open an issue describing your proposal. Please search existing issues first to avoid duplicates, and be clear about the problem you're solving and why it matters.
+
+Early feedback is encouraged before jumping into implementation.
+
+### Issues
+
+We use GitHub issues to track bugs, inconsistencies, or gaps in the specification. If you've found something that needs fixing, search open issues to see if someone else has reported the same thing. If it's new, open an issue — we'll use it to discuss the problem before any work begins.
+
+When reporting an issue, please include:
+
+- A clear and descriptive title
+- A detailed description of the problem
+- Links to relevant sections of the specification
+- Context or examples where possible
+
+### Pull requests
+
+Feel free to fork the repository and create a pull request for changes you think you can contribute — whether small fixes or larger spec changes.
+
+The team will review your pull request as soon as possible.
+
+## Working in this repository
+
+### Specification development
+
+The main specification source lives at [`specification/index.html`](./specification/index.html). This file uses [ReSpec](https://respec.org/docs/), the standard tool for authoring W3C specifications.
+
+You don't need a full development setup to contribute to the spec.
+
+#### Previewing changes
+
+Preview changes with `npx serve ./specification/` (or [any other static HTTP file server](https://gist.github.com/willurd/5720255)) and opening http://localhost:3000/index.html.
+
+#### Related specifications
+
+This repository also includes:
+
+- Web Monetization flows → [`specification/flows/`](./specification/flows/)
+- Browser extension API → [`specification/extensions-api/`](./specification/extensions-api/)
+
+#### Formatting
+
+Prettier is disabled for files under `specification/*`. W3C specifications follow a formatting style that conflicts with Prettier (for example, void elements without trailing slashes), and there is currently no clean way to align the two.
+
+#### Versioning
+
+This is a Community Group Draft, so iteration is expected. We only snapshot major versions of the specification — for example, the [2021-03-17 draft](./specification/versions/CG-DRAFT-web-monetization-20210317.html) currently lives in `specification/versions/`.
+
+### Website development
+
+For website development, [see here](https://github.com/WICG/webmonetization#get-set-up)
+
+## Submitting Pull Requests
+
+1. [Fork](https://github.com/WICG/webmonetization) the repository
+2. Create a new branch from `main`
+3. Make your changes and commit them
+4. Open a pull request to `main` with a clear title and description
+   - **Consider using [conventional commit](https://www.conventionalcommits.org/en/v1.0.0/) format** (e.g., `feat: add new API endpoint`, `fix: resolve validation error`)
+5. If your PR addresses an existing issue, reference it using `Closes #123`
+6. Be prepared to address feedback and make changes if needed
+
+**Contributor attribution (W3C requirement)**
 
 To add a contributor (other than yourself, that's automatic), mark them one per line as follows:
 
@@ -17,18 +96,12 @@ If you added a contributor by mistake, you can remove them in a comment with:
 -@github_username
 ```
 
-If you are making a pull request on behalf of someone else but you had no part in designing the feature, you can remove yourself with the above syntax.
-
-## Specification Development
-
-If you are interested in making changes to the specification, set up this repository on your local machine first. You can follow the [instructions on the README](./README.md#get-set-up), but you don't necessarily need to install dependencies or set up an environment if you want to work on the specification only (and not rest of the website).
-
-The source file for the specification document is at [specification/index.html](./specification/index.html). This is the raw ReSpec version that editors should make changes to. Documentation for ReSpec can be accessed on the [respec.org](https://respec.org/docs/).
-
-Preview changes with `npx serve ./specification/` (or [any other static HTTP file server](https://gist.github.com/willurd/5720255)) and opening http://localhost:3000/index.html.
+If you are submitting on behalf of someone else and didn't contribute directly, you can remove yourself using the same syntax.
 
-Similar to the main specification, there are also [Web Monetization flows](./specification/flows/) and the [browser extension API](./specification/extensions-api/) implementation specifications.
+### Review Process
 
-In general, Community Group Draft Reports do not follow the same strict conventions as more mature specifications. We only archive major versions of the specification. For example, a copy of the [2021-03-17 draft report](./specification/versions/CG-DRAFT-web-monetization-20210317.html) currently lives in [specification/versions/](./specification/versions).
+- Maintainers will review your PR for clarity, correctness, and alignment with the specification
+- Please respond to feedback promptly and make any necessary changes
+- Once approved, your changes will be merged into the main branch
 
-Prettier is disabled on `specification/*` as it conflicts with the code format style used by W3C specifications. There is [no way](https://github.com/prettier/prettier/issues/5246) to configure Prettier to follow the [W3C recommendation](https://github.com/validator/validator/wiki/Markup-%C2%BB-Void-elements) of not using trailing slashes on void elements.
+Thank you for contributing to Web Monetization! Join the conversation on [Slack](https://communityinviter.com/apps/interledger/interledger-working-groups-slack) to connect with other contributors and stay up to date on developments.